Back to EveryPatent.com
United States Patent |
5,198,762
|
Shimoe
,   et al.
|
March 30, 1993
|
Magnetic sensor having spaced magneto-resistance elements
Abstract
A magnetic sensor has first, second, third and fourth magneto-resistance
effect elements disposed in a direction of a magnetizing pitch (1) of a
magnetic recording medium serving to supply a magnetic signal, with first
and second magneto-resistance effect elements disposed spacedly from each
other at an interval corresponding to an electrical angle of .theta., the
third and fourth magneto-resistance effect elements disposed spacedly from
each other at an interval corresponding to an electrical angle of
(360.degree.-.theta.), and the intervals between the center line of the
first and second magneto-resistance effect elements and between the line
of the third and fourth magneto-resistance effect elements being set to
n.lambda.. The four magneto-resistance effect elements are connected to
one another in series in the order of the first, second, fourth and third
magneto-resistance effect elements with both ends of the
serially-connected magneto-resistance effect elements being provided with
a power source terminal, and an output terminal being provided at a
conjunctive point of the second and fourth magneto-resistance effect
elements. .theta. is set to a range of
30.degree..ltoreq..theta..ltoreq.90.degree., based on .lambda.=360 to
thereby enable an output wave form of the magnetic sensor to have a large
or sharp gradient in the vicinity of a comparing level.
Inventors:
|
Shimoe; Osamu (Kumagaya, JP);
Shonowaki; Yukimasa (Kumagaya, JP)
|
Assignee:
|
Hitachi Metals, Ltd. (Tokyo, JP)
|
Appl. No.:
|
818340 |
Filed:
|
January 9, 1992 |
Foreign Application Priority Data
Current U.S. Class: |
324/207.21; 338/32R; 360/315 |
Intern'l Class: |
G01B 007/14; G11B 005/37 |
Field of Search: |
324/207.21,235,252
307/309
338/32 R,32 H
360/113
|
References Cited
U.S. Patent Documents
4731580 | Mar., 1988 | Indo | 324/252.
|
4818939 | Apr., 1989 | Takahashi et al. | 324/252.
|
5036276 | Jul., 1991 | Aizawa | 324/207.
|
5047716 | Sep., 1991 | Katagiri | 324/207.
|
Foreign Patent Documents |
54-41335 | Nov., 1973 | JP.
| |
2-16973 | Dec., 1982 | JP.
| |
63-302319 | Jun., 1987 | JP.
| |
Primary Examiner: Strecker; Gerard R.
Assistant Examiner: Edmonds; Warren S.
Attorney, Agent or Firm: Finnegan, Henderson, Farabow, Garrett & Dunner
Claims
What is claimed is:
1. A magnetic sensor for detecting a magnetic signal from a magnetic
recording medium magnetized periodically in a magnetizing direction at a
magnetizing pitch of .lambda. on the basis of variation in resistance
value of magneto-resistance effect elements, comprising:
first, second, third and fourth magneto-resistance effect elements disposed
in this order in the magnetizing direction of the magnetizing pitch
.lambda. of the magnetic recording medium, wherein said first and second
magneto-resistance effect elements are disposed spacedly from each other
at an interval corresponding to an electrical angle of .theta., based on
.lambda.=360.degree., while said third and fourth magneto-resistance
effect elements are disposed spacedly from each other at an interval
corresponding to an electrical angle of (360.degree.-.theta.), and wherein
the interval between a center line of said first and second
magneto-resistance effect elements and a center line of said third and
fourth magneto-resistance effect elements is set to n.lambda. (n: an
integer), said four magneto-resistance effect elements being connected to
one another in series in the order of said first, second, fourth and third
magneto-resistance effect elements and .theta. being set to a range of
30.degree..ltoreq..theta..ltoreq.90.degree., and wherein a power source
terminal is provided at each end of said serially-connected
magneto-resistance effect elements and an output terminal is provided at a
connection point of said second and fourth magneto-resistance effect
elements.
2. A magnetic sensor assembly comprising a plurality K of magnetic sensors
as claimed in claim 1, wherein said K magnetic sensors are disposed
spacedly from one another at an interval of (1+m/2+1/(2K)) .lambda. (1, m:
0 or an integer, K: an integer, .lambda.: magnetizing pitch), and wherein
the individual outputs of said K magnetic sensors are synthesized into a
composite output.
3. The magnetic sensor as in claim 1, wherein .theta. is in range
45.degree.<.theta.<90.degree..
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetic sensor for detecting a magnetic signal
from a magnetic recording medium utilizing variation in the resistance
value of a magneto-resistance effect element.
2. Description of the Related Art
In order to detect a magnetic signal from a magnetic recording medium,
there has been utilized a magnetic sensor in which the magnetic signal is
converted to an electrical signal by a magneto-resistance effect element
and then the electrical signal is subjected to processing. This type of
magnetic sensor has been disclosed in Japanese Unexamined Published
(Laid-open) Patent Application No. Sho-54-41335. In this magnetic sensor,
a pair of comb-shaped patterns are disposed so as to be perpendicular to a
plane containing a magnetized pattern on a magnetic recording medium
(hereinafter referred to as "magnetized pattern plane) which has been
periodically magnetized at a pitch .lambda. of magnetic poles (hereinafter
referred to as "magnetizing pitch") in such a manner as to be positionally
deviated by .lambda./2 on a plane in parallel with the direction of the
magnetized pattern. However, in the manner as described above, when the
magnetized pattern is so designed as to have an extremely minute
magnetizing pitch .lambda. in order to improve resolution, the intensity
of a rotating magnetic field within a plane containing the comb-shaped
patterns is weakened and thus the magneto-resistance effect element can
not be magnetized to saturation. Therefore, this magnetic sensor has the
shortcoming that a satisfactory detection can not be performed.
In order to overcome the above shortcoming, there has been further proposed
a magnetic sensor in which two magneto-resistance effect elements are
disposed in parallel to the magnetized pattern plane, but perpendicular to
the magnetizing direction of the magnetized pattern, as disclosed in
Japanese Examined Published Patent Application No. Hei-2-16973. In this
case, in the same manner as shown in FIG. 6, N and S magnetic poles are
alternately disposed on the magnetic recording medium at an interval of
.lambda., and two striped magneto-resistance effect strip-shaped elements
are disposed spacedly from each other at an interval of .lambda./2. The
two magneto-resistance effect elements are connected to each other in
series, and both ends of the serially-connected elements are provided with
a power source terminal. An output of these magneto-resistance effect
elements is obtained at an output terminal which is provided to a
conjunctive point of the elements. When a current flows through the
magneto-resistance effect elements while a magnetic field is applied to
the elements in a direction perpendicular to a direction of the current, a
resistance value between both terminals of the elements varies as shown in
FIG. 5. As is apparent from FIG. 5, if an area which is not magnetically
saturated (hereinafter referred to as "non-saturation area") is utilized
in the resistance-variation rate as shown in FIG. 5, a substantially
sinusoidal output can be obtained. This magnetic sensor utilizes the above
characteristic. That is, since the intensity of a magnetic field which is
applied to the magneto-resistance effect elements varies in a sinusoidal
form by rotating the magnetic recording medium or the like, the output
waveform of the resistance-variation which is obtained at the output
terminal is also substantially sinusoidal. The thus obtained sinusoidal
output is subjected to waveform processing to be converted to a
rectangular waveform, whereby variation of the magnetic signal is
detected.
This magnetic sensor is required to actuate the magneto-resistance effect
element while the output of the element is not saturated and to output a
sinusoidal-waveform signal at the output terminal. Therefore, the gap
between the magnetic recording medium and the magnetic sensor is set to be
relatively large, and thus the intensity of the magnetic field which is
applied to the magnetic sensor is weakened. However, there are some cases
where the gap between the magnetic recording medium and the magnetic
sensor must be set to a short distance. In these cases, the intensity of
the magnetic field which is applied to the magnetic sensor is
unintentionally excessively strengthened, so that the magneto-resistance
effect element is saturated and the output waveform thereof is extremely
distorted. Therefore, in the waveform shaping operation of the sinusoidal
waveform to the rectangular waveform, the gradient of the output
sinusoidal voltage is moderated in the vicinity of a comparing level as
indicated by a dotted circle of FIG. 7. For example, the output signal of
rectangular waveform greatly varies merely when the comparing level is
slightly fluctuated (within plus or minus 8 mV) due to the temperature
drift of a processing circuit or the like, and thus it is difficult to
detect a magnetized position.
The distance of the gap between the magnetic recording medium and the
magnetic sensor is mainly dependent on design accuracy of the magnetic
recording medium, but is also dependent on unavoidable factors such as
eccentricity of the axis of the magnetic recording medium and so on.
Therefore, there has been required a magnetic sensor for obtaining an
output signal having a large or sharp gradient in the vicinity of the
comparing level.
In order to satisfy the above requirement, a magnetic sensor as disclosed
in Japanese Unexamined Published Patent Application No. Sho-63-302319 has
been proposed. This magnetic sensor comprises two pairs of patterns
confronting a magnetic recording medium having a magnetizing pitch of
.lambda., one of which patterns includes two magneto-resistance effect
elements disposed at an interval of i.lambda. and the other of which
includes two magneto-resistance effect elements disposed at an interval of
(i+j).lambda., where i represents zero or an integer and 0<j<1). In this
magnetic sensor, an output waveform obtained through add and subtract
operations between outputs of the above pairs has a large gradient in the
vicinity of the comparing level.
For example, as shown in FIG. 8, N and S magnetic poles are alternately
disposed on a magnetic recording medium 21 at an interval of .lambda., and
a pair of magneto-resistance effect elements 22 and 23 which are disposed
spacedly at an interval of 0.2.lambda. in such a manner as to confront the
magnetic recording medium, are connected to each other in series. Both
ends of the elements are supplied with a voltage from a power source, and
an output having a waveform as indicated by a character A of FIG. 9 is
obtained at a connection point A of the magneto-resistance effect
elements.
Likewise, a second pair of magneto-resistance effect elements 25 and 26
which are disposed spacedly at an interval of 0.8.lambda. in such a manner
as to confront the magnetic recording medium, are connected to each other
in series, and both ends of the connected elements are supplied with a
voltage from the power source, to thereby obtain an output waveform as
indicated by a character B of FIG. 9 at a conjunctive point B. In this
case, in order to provide both outputs of the magneto-resistance effect
elements with a suitable relative phase-difference, both pairs are
positionally deviated from each other by 0.7.lambda.. A final output
having a waveform as shown in FIG. 10 is obtained by adding both of the
outputs A and B of the pairs.
The magnetic sensor thus constructed is superior in that the output of the
magnetic sensor has a larger or sharper waveform in the vicinity of the
comparing level, in comparison with a conventional magnetic sensor in
which two pairs of magneto-resistance effect elements, one pair comprising
two magneto-resistance, effect elements disposed at the interval of
.lambda., are spacedly disposed at an interval of (N+1/2).lambda..
However, in the magnetic sensor using two pairs of magneto-resistance
effect elements as described above, an alternating arrangement is required
for current terminals, for example, in such a manner that Vcc, GND, Vcc
and GND are alternately disposed as shown in FIG. 8. The current terminals
are not integrally or commonly formed on substrate, so that a wire pattern
in which four current terminals are individually electrically drawn out of
the respective magneto-resistance effect elements is required and thus
there is a probability that each element would be required to be large in
size. Further, there frequently occur unfavorable results in manufacturing
process and practical use because connection is required for the
magneto-resistance effect elements. Still further, since the magnetic
sensor adopting the above manner does not function as a magnetic sensor
unless an adder for adding the outputs 1 and 2 of the two pairs of
magneto-resistance effect elements is included in the device, high cost
and complicated construction are required to apply the above magnetic
sensor to a field in which plural magnetic sensors must be used.
SUMMARY OF THE INVENTION
An object of this invention is to provide a magnetic sensor capable of
overcoming the above disadvantages of conventional magnetic sensors.
In order to attain the above object, the magnetic sensor according this
invention includes first, second, third and fourth magneto-resistance
effect elements which are disposed in this order in a direction of a
magnetizing pitch (.lambda.) of a magnetic recording medium serving to
supply a magnetic signal, wherein the first and second magneto-resistance
effect elements are disposed spacedly from each other at an interval
corresponding to an electrical angle of .theta., the third and fourth
magneto-resistance effect elements are disposed spacedly from each other
at an interval corresponding to an electrical angle of
(360.degree.-.theta.), where 360.degree. corresponds to the electrical
angle of the pitch interval (.lambda.) an interval between a center line
of the first and second magneto-resistance effect elements and a center
line of the third and fourth magneto-resistance effect elements is set to
n.lambda.. The four magneto-resistance effect elements are connected to
one another in series in the order of the first, second, fourth and third
magneto-resistance effect elements. Both ends of the serially-connected
magneto-resistance effect elements are provided with a power source
terminal, and an output terminal is provided at a connection point of the
second and fourth magneto-resistance effect elements. .theta. is set to a
range of 30.degree..ltoreq..theta..ltoreq.90.degree..
Further, an assembly of K magnetic sensors as described above are disposed
spacedly from one another at intervals of (1+m/2+1/(2K)).lambda. (1, m: 0
or an integer, K: an integer, .lambda.: magnetizing pitch), and outputs of
the magnetic sensors are synthesized into a composite output.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an explanatory diagram for a first embodiment of a magnetic
sensor;
FIGS. 2(a)-2(g) are a waveform diagram for an output waveform of each
magneto-resistance effect element, a composite waveform and a composite
output;
FIG. 3 is a diagram for an output waveform in a case where the magnetic
sensor of the first embodiment is used;
FIGS. 4a to 4e are explanatory diagrams and waveform diagrams for a
magnetic sensor of a second embodiment;
FIG. 5 is a characteristic diagram for a conventional magneto-resistance
effect element;
FIG. 6 is an explanatory diagram for a magnetic sensor using two
conventional magneto-resistance effect elements;
FIG. 7 is a diagram for an output waveform of a conventional magnetic
sensor;
FIG. 8 is an explanatory diagram for a magnetic sensor using four
conventional magneto-resistance effect elements;
FIG. 9 is a waveform diagram for a composite output of two
magneto-resistance effect elements of a conventional magnetic sensor; and
FIG. 10 is a waveform diagram for a composite output of four
magneto-resistance effect elements of a conventional magnetic sensor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of this invention will be described in more detail
with reference to the accompanying drawings.
FIG. 1 is an schematic diagram for the construction of a magnetic sensor
according to this invention.
A magnetic recording medium 1 has a magnetized pattern in which different
magnetic poles (S and N) are alternately periodically arranged at a
magnetizing pitch of .lambda., and a magnetic sensor is disposed so as to
confront a magnetized portion through a gap to detect variation of a
magnetic signal from the magnetized portion.
The magnetic sensor comprises first, second, third and fourth
magneto-resistance effect elements MR1, MR2, MR3 and MR4 which are
disposed in this order in a direction of the magnetizing pitch. The first
and second magneto-resistance effect elements MR1 and MR2 are disposed
spacedly from each other at an interval corresponding to an electrical
angle of .theta., and the third and fourth magneto-resistance effect
elements MR3 and MR4 are disposed spacedly from each other at an interval
corresponding to an electrical angle of 360.degree.-.theta.. In addition,
these four magneto-resistance effect elements are disposed such that an
interval between a center line of the first and second magneto-resistance
effect elements and a center line of the third and fourth
magneto-resistance effect elements is equal to n.theta. (n: an integer, in
this case to .theta.). The four magneto-resistance effect elements MR1,
MR2, MR3 and MR4 are connected to one another in series in the order of
the first, second, fourth and third magneto-resistance effect elements.
Both unconnected ends of these serially connected magneto-resistance
effect elements serve as a terminal for a power source (power source
terminal), and an output terminal 2 for the serial-connected elements is
provided at a conjunctive portion of the second and fourth
magneto-resistance effect elements MR2 and MR4. The output terminal 2
outputs a sum value between a composite output in resistance variation of
the first and second magneto-resistance effect elements MR1 and MR2 and
another composite output in resistance variation of the third and fourth
magneto-resistance effect elements MR3 and MR4.
The magneto-resistance effect elements MR1 and MR2 develop
voltage-variations as shown in FIGS. 2(a) and 2(b) respectively because
the voltage-variation of the magneto-resistance effect element MR2 is
delayed by .theta. with respect to the voltage-variation of the
magneto-resistance effect element MR1, and a composite output voltage V1
of the magneto-resistance effect elements MR1 and MR2 has a waveform as
shown in FIG. 2(c).
On the other hand, the magneto-resistance effect elements MR3 and MR4
develop voltage-variations as shown in FIGS. 2(d) and 2(e) which are
expected from the positional relationship thereof as shown in FIG. 1. That
is, the voltage-variation of the magneto-resistance effect element MR3 has
an output waveform whose phase proceeds by (360.degree.-.theta.)/2 from a
phase point which is further delayed by .lambda. (corresponding to an
electrical angle of 2.pi.=360.degree.) from a midpoint of a phase
difference .theta. between the output wave forms of the magneto-resistance
effect elements MR1 and MR2 (in other words, a phase point delayed from
the output of MR1 by .theta./2), while the voltage-variation of the
magneto-resistance effect element MR4 has an output waveform whose phase
is delayed from the phase point by (360.degree.-.theta.)/2. The composite
output voltage V2 of the output waveforms becomes a waveform as shown in
FIG. 2(f). Therefore, the composite output V of the output voltages V1 and
V2 as described above has a waveform as indicated by a solid line of FIG.
2(g). This waveform of the composite output V has a extremely large or
sharp gradient in the vicinity of the comparing level, so that a
rectangular waveform which is obtained from the obtained output waveform
scarcely varies even when the comparing level drifts slightly, and thus
the detection accuracy is improved.
EXAMPLE 1
FIG. 3 shows an output waveform of the magnetic sensor as shown in FIG. 1,
which was obtained by changing .theta. from 0.degree. to 90.degree. every
degree interval of 15.degree.. As is apparent from FIG. 3, the gradient of
the output waveform becomes larger in the vicinity of the comparing level
as .theta. is increased. By setting .theta. above 30.degree. and
preferably above 45.degree. in practical use, the magnetic sensor is not
influenced by fluctuation of the output and noises in the waveform shaping
operation to the rectangular waveform, and variation in ratio of ON and
OFF of an output signal and position variation are small, so that the
detection accuracy is improved. On the other hand, the gradient of the
output waveform in the vicinity of the comparing level is larger, but an
output value is reduced as .theta. approaches 90.degree., and therefore it
is clear that it is preferable to set .theta. below 90.degree..
As described above, in this invention, the improvement of the output
waveform is enabled without sacrificing amplitude of the output by
satisfying the following condition:
30.degree..ltoreq..theta..ltoreq.90.degree.. Further, the magnetic sensor
of this invention comprises four magneto-resistance effect elements, but
has the advantage that it may be applied without a special processing
circuit to a field in which plural magnetic sensors are suitably combined
with one another because the magnetic sensor is substantially a
three-terminal element.
EXAMPLE 2
Another embodiment of the magnetic sensor of this invention will be next
described with reference to FIG. 4.
In this embodiment, five magnetic sensors of the first embodiment are used
in combination to obtain high resolution. In FIG. 4, each of magnetic
sensors Sa to Se comprises four magneto-resistance effect elements MR1 to
MR4 used in the first embodiment as described above. In this case, .theta.
is set to 60.degree.. The magnetic sensors Sa to Se are disposed spacedly
from one another at an interval of 5/8.lambda. in the direction of the
magnetizing pitch (.lambda.) of the magnetic recording medium 1. Of the
outputs Va, Vb, Vc, Vd and Ve of the magnetic sensors Sa, Sb, Sc, Sd and
Se, each pair of the outputs of the neighboring magnetic sensors are
connected to a synthesizer (not shown) to obtain add-and-subtract outputs
I, II, III, IV and V thereof. A spacing interval between the neighboring
magnetic sensors, for example, Sa and Sb may be set to (n+5/8).lambda. (n:
an integer) because phase is not varied.
A high-resolution increment signal is intensively required in a rotating
magnetic sensor. However, in a case where the resolution is improved with
the same drum diameter, the magnetizing pitch .lambda., and thus the
output magnetic flux from the drum surface is reduced. As a result, a gap
between the sensor and the drum is narrowed, and there occurs a
disadvantage that the assembling process is difficult. However, according
to this invention, high resolution is obtained without varying the gap
dimension between the sensor and the drum (without shortening the
magnetizing pitch).
As described above, in this embodiment, the respective magnetic sensors are
disposed at the interval of (5/8).lambda. for the magnetizing pitch
.lambda. of the drum. Therefore, the output signals Va, Vb, Vc, Vd and Ve
of the respective magnetic sensors are delayed by (5/8).lambda.,
respectively, as shown in FIG. 4(b).
As is apparent from the first embodiment, the output of the magnetic sensor
according to this invention contains higher harmonic waves. However, in
order to simplify the description, the principle of a process of obtaining
the above output signals will be described considering only a fundamental
wave.
For example, assuming that Va=V sin .theta., since a phase difference
between the respective output signals is (5/8).lambda.,
##EQU1##
Likewise,
II=Vc-Vb=2V sin 5.pi./8.multidot.sin (.theta.-3.pi./8)
III=Vc-Vd=2V sin 5.pi./8.multidot.sin (.theta.-5.pi./8)
IV=Ve-Vd=2V sin 5.pi./8.multidot.sin (.theta.-7.pi./8)
Therefore, four waveforms having a phase difference of 45.degree.
therebetween are obtained through the synthesizing process. FIG. 4(c)
shows the signals I (=Va-Vb) and III (=Vc-Vd) which are obtained by
synthesizing the output waveforms as shown in FIG. 4(b), and FIG. 4(d)
shows rectangular waveforms which are obtained by subjecting the signals I
and III to waveform shaping and then to an exclusive OR processing. As is
apparent from FIG. 4, in a manner of subjecting the original waves and
composite waves to the waveform shaping and the exclusive OR processing
after other processings for the waves, a final composite signal
(hereinafter referred to as "processed signal") having a period of
(1/2).lambda. can be obtained.
The processed signal waveforms having a phase difference of 45.degree. (of
the original wave) are synthetically obtained as A-phase and B-phase
signals from I and III and from II and IV, respectively, and the A-phase
and B-phase signals have a half period of the original waves and a phase
difference of 90.degree..
The waveforms of the signals I to IV and a phase relationship after
processed are shown in FIG. 4(e). According to this invention, a
high-resolution magnetic sensor-assembly can be easily implemented by
merely disposing plural unit magnetic sensor patterns at a predetermined
pitch.
According to the magnetic sensor of this invention as described above,
since four magneto-resistance effect elements are disposed with a
predetermined arrangement while connected to one another in series and an
interval of the respective magneto-resistance effect elements is set to a
suitable value, an output waveform has a large or sharp gradient in the
vicinity of the comparing level and has a large output value (amplitude).
As a result, the detection accuracy of the magnetic sensor is improved.
Further, four magneto-resistance effect elements are used, but only two
terminals are used as a power source terminal, and this is advantageous
for the manufacturing process and practical use of the sensor. Still
further, in a case where plural magnetic sensors each comprising four
magneto-resistance effect elements as described above are disposed
spacedly from each other at a predetermined interval and a composite
output between the respective magnetic sensors is obtained, high
resolution is obtainable and thus the detection accuracy can be improved.
Top